Exposed scrollEnabled on TextInput (#19330)

Summary:
On iOS, it is not possible to select a range of text using a `Text` component (see #13938). Because of how the `Text` component is implemented on iOS, this will not work without a complete re-write. On Android however, this is not an issue.

As the `TextInput` component has evolved, it can more or less be used as a drop-in replacement on iOS by setting `multiline={true}` and `editable={false}`. Except for one detail: the text input field has scrolling activated and it's not possible to turn off. (See #1391 and #15962).

This pull request addresses that issue, simply by exposing the `scrollEnabled` property:

```
<TextInput
    multiline
    editable={false}
    scrollEnabled={false}
  />
```

1. Create a multiline `TextInput` component, with the attributes presented above.
2. Run on iOS
3. The `TextInput` field should not be able to scroll

facebook/react-native-website#367

[IOS] [FEATURE] [TextInput] - Made it possible to turn off scrolling on a multiline TextInput component
Pull Request resolved: #19330

Differential Revision: D9235061

Pulled By: hramos

fbshipit-source-id: 99d278004fc236b47dde7e61d74c71e8a3b9d170

Libraries/Components/TextInput/TextInput.js

@@ -581,6 +581,12 @@ const TextInput = createReactClass({
  * The text color of the placeholder string.
  */
  placeholderTextColor: ColorPropType,
+ /**
+ * If `false`, scrolling of the text view will be disabled.
+ * The default value is `true`. Does only work with 'multiline={true}'.
+ * @platform ios
+ */
+ scrollEnabled: PropTypes.bool,
  /**
  * If `true`, the text input obscures the text entered so that sensitive text
  * like passwords stay secure. The default value is `false`. Does not work with 'multiline={true}'.

Libraries/Text/TextInput/RCTBaseTextInputViewManager.m

@@ -48,6 +48,7 @@ @implementation RCTBaseTextInputViewManager
 RCT_REMAP_VIEW_PROPERTY(spellCheck, backedTextInputView.spellCheckingType, UITextSpellCheckingType)
 RCT_REMAP_VIEW_PROPERTY(caretHidden, backedTextInputView.caretHidden, BOOL)
 RCT_REMAP_VIEW_PROPERTY(clearButtonMode, backedTextInputView.clearButtonMode, UITextFieldViewMode)
+RCT_REMAP_VIEW_PROPERTY(scrollEnabled, backedTextInputView.scrollEnabled, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(blurOnSubmit, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(clearTextOnFocus, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(keyboardType, UIKeyboardType)